The invention relates to a sensing probe apparatus used for measuring the electrical field strength of a near field; particularly an extremely small sensitive probe for sensing the precise local near field of a complex electronic circuit device.
Electronic circuit devices require strict controls and limits related to electrical leakage, radio frequency emissions and interference. Such devices include densely arranged electronic components, conductors and circuitry which can produce numerous discreet electrical and magnetic fields which combine to form a total field strength. Near field sensing probes are utilized to analyze such electronic devices to determine the source of any electrical energy leakage so that the device can be modified to eliminate or reduce such leakage.
Presently available field strength sensing probes are limited in effectiveness because of their relatively bulky sensing tips measuring from about 0.5 inches to 1.0 inches. Such sensing probes also typically incorporate loop antennas as described in a publication dated May 17, 1984 in EDN by Scott Roleson entitled "Evaluate EMI Reduction Schemes With Shielded-Loop Antennas", and as illustrated in U.S. Pat. No. 4,277,744 and U.S. Pat. No. 4,588,993. Such probes operate on a principle which picks up the magnetic fields as a measured signal component which is an indirect method of locating the true source of the electrical field leakage. In addition, loop antenna probes are very sensitive as to the direction and orientation of the tip of the probe. Such probes also usually incorporate circuitry having common mode current on the shield return and are therefore affected by the potential of the operator.
It is an object of the present invention to provide an electrical field sensing probe which is extremely sensitive and which has a small compact sensor tip to sense the electrical field strength in precisely small regions of the electronic device.
It is an other object to provide a sensing probe which is not significantly affected by magnetic fields and not affected by the potential of the operator.